The devices disclosed in the following patents are representative of prior attempts to provide an in-the-hull mount for an underwater signal transducers of a marine vessel:
U.S. Pat. No. 1,394,482, issued Oct. 18, 1921 (Fessenden); PA1 U.S. Pat. No. 2,407,240, issued Sep. 10, 1946 (Barber); PA1 U.S. Pat. No. 2,469,594, issued May 10, 1949 (Danforth); PA1 U.S. Pat. No. 2,813,591, issued Nov. 19, 1957 (Smaltz et al.); PA1 U.S. Pat. No. 2,829,360, issued Apr. 1, 1958 (Allyn); PA1 U.S. Pat. No. 3,426,725, issued Feb. 11, 1969 (Gerhardsen); PA1 U.S. Pat. No. 4,282,590, issued Aug. 4, 1981 (Wingate); PA1 British patent No. 897,739, dated Oct. 10, 1958 (Electroacoustic GmbH); and PA1 Federal Republic of Germany Auslegeschrift 1 096 255, dated Dec. 29, 1960 (Electroacustic GmbH). PA1 "There may also be provided an automatic supervision device, which ensures pressure supply to the device 15 if the pressure therein should fall below a certain value. Such supervision device may also be so arranged as to reduce the pressure in the device 15, to the effect that the cup member 12 may yield somewhat, in order to reduce the effects of blows against the cup, if the vessel is operating in a heavy sea."
In each instance, the object is to provide a recessed housing or "sea chest" from which the transducer is projected. To avoid damage by collision with the bottom or debris, the transducer can be retracted into the sea chest to a position above the bottom of the hull. In the devices of the patents listed above and in equivalent in-the-hull mounts currently available, when actuated to the projected position the transducer is held in such position rigidly or substantially rigidly, such as by a rack-and-pinion or spindle drive or a hydraulic jack. The transducer and its mounting structure are vulnerable to damage if excessive force is applied. In the device disclosed in the Gerhardsen patent, the transducer is mounted in a "cup member" which can be swung to a projected position by operation of a hydraulic jack and ". . . there is provided lock means 19 for the purpose of locking the cup member in the lowermost position . . . " (column 3, lines 10-12). As explained in the paragraph beginning at column 3, line 15,
Gerhardsen does not explain how to achieve such "yielding". In the device disclosed in that patent, the transducer assembly is held substantially rigidly in its projected position and is as vulnerable to damage by collision with the bottom or debris as the devices of the other patents listed above, particularly if struck from the rear or the side as could occur while the vessel is turning, drifting or operating in reverse.